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Many of the patches are simple integer constant replacements, whereas that particular patch rewrites the assembly code for the function that controls line spacing, so if Kobo makes any changes to related functions, it could not only change the position of the line spacing function within the library, but it could also change which registers are being used, thus requiring significant alterations to the assembly instructions being added with the patch.
It's the kind of thing that Kobo can change trivially with access to the source code, but trivial changes to source code can cause the compiler to make significantly different decisions, and the resulting assembly can be incompatible with a previous version of the same patch.
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